The present invention is related to a method for the operation of a wind energy plant with a rotor, which transfers a driving moment to a generator via a drive train, wherein the generator provides a pre-settable generator moment acting opposite to the driving moment, and is connectable to a grid.
Such wind energy plants are normally connected to a power supply grid of an electric utility and feed electric power into the power supply grid. In doing so, the wind energy plants provide active power and reactive power, and can perhaps perform a contribution for the stabilisation of the power supply grid.
The demands made by the electric utilities for the wind energy plants are specified in detailed grid connection rules. In this matter, the demands for the behaviour of wind energy plants at voltage dips in the grid have greatly changed in the last years. While in the past, the wind energy plants had to be separated from the grid as fast as possible at a voltage dip, actual grid connection rules prescribe that the wind energy plants must remain connected to the grid at certain voltage dips, in order to support the grid through the supply of reactive power. For instance, the grid connection rules may prescribe that the wind energy plant is not to be separated from the grid at a voltage dip, wherein the voltage remaining in the grid is greater than 15% of the rated voltage and which does not exceed a certain period of time.
However, special protection measures have to be taken in order to avoid a damage or destruction of the electric components of the wind energy plant, when the same remain connected to the grid during sudden changes of the voltage of the grid.
A generator system with a corresponding protection device and a method for the operation of the generator system are known from WO 204/030199 The known generator system has a double-fed three-phase generator with grid-coupled stator coil and at least one rotor coil. In the known method, the current flow in the stator circuit is interrupted through the activation of a fast cut-off unit after the detection of a sudden change of the voltage of the grid. Thereafter, the generator is synchronised with the actual grid voltage again and the current flow between grid and stator is permitted again. Through this measure, an electric overload of the components of the generator system is avoided.
However, when using such a generator system in a wind energy plant, the mechanical stresses occurring during a voltage change must also be taken into account. For instance, most notably sharp changes of the generator moment occur as a consequence of sudden voltage changes, which leads to a high mechanical stress of the elements of the drive train, for instance, in the context of the great lag coefficients of the movable parts of a wind energy plant.
On the basis of this, it is the objective of the present invention to provide a method for the operation of a wind energy plant which reduces those mechanical stresses of the components of the wind energy plant which are due to sudden changes of the grid voltage.